Conventionally, a shock absorber has been proposed that absorbs applied load through plastic deformation by being folded back in the axial direction thereby absorbing impact energy. Such axial folding deformation is known as turning deformation. For example, Patent Document 1 discloses a shock absorber including a metal pipe, in which a small diameter portion (2a) is continuous with a large diameter portion (2b) with a tapered portion (3) in between. The length of the large diameter portion (2b) is set to be substantially half the length of the small diameter portion (2a), and the small diameter portion (2a) is accommodated in the large diameter portion (2b) when the small diameter portion (2a) is subjected to turning deformation that starts at the tapered portion (3). This reduces the space behind the large diameter portion (2b) or the shock absorber that is required for allowing turning deformation.